Case Study 52

1. Case Study 52 Edward D. Plowey

2. The patient is a 48 year old woman with a 3-year history of migraine headaches and recent development of a subtle right visual field loss. The patient underwent an MRI of the brain to further investigate a potential cause of these symptoms. Case History

3. Question 1 Describe the radiologic abnormality in the following MRI images.

4. T2 FLAIR T1 T1 POST-CONTRAST

5. Answer T1 weighted images show an extra-axial parafalcine mass lesion impinging on regions of the left parietal and occipital lobes. The tumor exerts mass effect that distorts the left lateral ventricle and induces considerable parenchymal vasogenic edema. The tumor shows avid contrast enhancement and appears to show a dural tail on the post-contrast T1-image.

6. Question 2 What is the differential diagnosis for this lesion?

7. Answer The differential diagnosis of this lesion includes: Meningioma Hemangiopericytoma Solitary Fibrous Tumor Alternative dural-based mesenchymal neoplasm Metastasis

8. Question 3: Intraoperative Consultation • The patient was taken for tumor resection. An intraoperative consultation was requested to confirm the clinical impression of meningioma. • A smear preparation yielded tightly cohesive fragments of fibrous tissue with moderate cellularity (see image to right). A frozen section was subsequently prepared. • Describe the findings in the virtual frozen section and render a frozen section diagnosis.

9. Answer • A frozen section demonstrates a moderately cellular neoplasm. The tumor cells show oblong to spindle nuclei with speckled chromatin and a loose interlacing fascicular growth pattern focally. The tumor lacks a lobular growth pattern. An area of microcystic degeneration versus ice crystal artefact is seen. A hypocellular area with prominent broad bundles of collagen is seen. No intranuclear pseudo-inclusions or meningothelial whorls are seen. Mitotic figures and necrosis are not seen in the frozen section. • Intraoperative diagnosis: A. Neoplastic B. Low grade spindle cell neoplasm

10. Question 4: Permanent Sections Examine the following virtual permanent section slides and delineate a panel of special stains: Permanent of Frozen Section Tissue Additional Permanent Section

11. Answer • Histologic sections resemble the frozen section and raise the following differential diagnosis: • Meningioma (deplete of whorls) • Hemangiopericytoma / Solitary Fibrous Tumor • Question 5: • What panel of immunostains will you order to differentiate among these entities?

12. Answer • Histologic sections resemble the frozen section and raise the following differential diagnosis: • Meningioma (deplete of whorls) • EMA (click to view the virtual slide) • Hemangiopericytoma / Solitary Fibrous Tumor • CD34 (click to view the virtual slide) • bcl-2 (click to view the virtual slide) • Reticulin (click to view the virtual slide) • Ki67 (click to view the virtual slide)

13. Question 6 What information do the special stains convey? What is the final diagnosis?

14. Answer • The EMA immunostain is entirely negative, which argues against the diagnosis of meningioma. • The tumor shows moderate to strong and diffuse staining for CD34 and Bcl-2. A Ki67 immunostain shows a low proliferative index (3-4%). • A reticulin stain shows that in many areas, the tumor is lacking in single-cell pericellular reticulin deposition. • Diagnosis: SOLITARY FIBROUS TUMOR.

15. Discussion Compared to meningioma, solitary fibrous tumor (SFT) is a relatively rare neoplasm, but it should always be considered in the differential diagnosis of a contrast-enhancing dural-based mass. The key diagnostic features of SFT are a ovoid to spindle cells neoplasm with a “patternless” growth pattern and usually prominent collagen deposition. In contrast to meningioma, which is immunoreactive for EMA, SFT is usually positive for CD34 and Bcl-2. CD34 immunoreactivity in SFT has been proposed to be related to origin from dural fibroblasts. CD34 immunoreactivity in some meningiomas may be related to fibroblast inclusion in the neoplasm. • Cummings et al. Acta Neuropathol. 102:349-354, 2001.

16. Discussion SFT and hemangiopericytoma (HPC) demonstrate several overlapping histomorphologic features. Some experts favor lumping the two into a single diagnostic category HPC-SFT in which the two entities represent ends of a morphologic spectrum of a single entity, especially when dealing with non-central nervous system tumors. Evidence supports a vital distinction between SFT and HPC in the central nervous system (Tihan et al. Arch Pathol Lab Med. 127:432-9, 2003). CNS SFT is an indolent tumor that only occasionally recurs following resection. CNS HPC usually recurs and often metastasizes outside the central nervous system to evoke considerable morbidity and even mortality.

17. Discussion Reticulin staining pattern in a case of dural hemangiopericytoma. HPC often shows more densely-packed, chaotically arranged cells and fewer areas of broad collagen bundle deposition. A key distinguishing feature is the rich reticulin network surrounding single tumor cells in HPC (see example image to the right) that is not seen in SFT.